MIDP-9 "Procedures for Treatment, Prevention, and/or Control of Parasitic Infections" Schistosomiasis remains one of the most significant parasitic diseases in the world, particularly in the rural agrarian third world. Current development of expanded agricultural programs utilizing perennial irrigation schemes and water impoundment have promoted the spread of this disease. Development of vaccines has been slow for this and other well-known protozoan and helminthic infections. A most promising approach has been utilization of radiation-attenuated cercariae or schistosomula which is intended to stimulate antibody production in the host without resulting in a full-scale infestation or further propagation of the parasite. Results to date have not been definitive enough to justify adoption of this approach as a method of prevention or control. In preparing the irradiated vaccines, low Linear Energy Transfer (LET) radiation (x-rays and electrons) have been used. We believe a significant improvement in reliability of results (sterility and inhibition of growth along with adequate host antibody production) can be achieved by use of high LET radiation (protons, neutrons, or heavier charged particles). The relatively high mutagenicity vs. kill of high LET radiation has been well established. Should this approach prove correct, we believe the probability of preparing a longer-lived vaccine is enhanced. We are not aware of any other study using this approach. The principal investigators have had extensive experience in the applications of radiation in general and in the specific requirements for a vaccine. Should the results of Phase I prove positive, it would lead to a Phase II effort directed toward achieving acceptance and reliable, reproducible production. The commercial value of irradiated organism vaccines in veterinary medicine has already been well demonstrated. Preliminary discussions with princpals of a major U.S. pharmaceutical organization indicates that there could be significant interest in development, manufacture, and distribution of the vaccine. The greatest interest will be within those organizations working with biologicals. A reliable, safe, and longer-lived vaccine based on irradiated immature schistosomes will be utilized extensively.